The body control module (BCM) supplies a voltage reference through the instrument panel (I/P) dimming voltage reference circuit to the interior lamp dimmer switch, which is part of the headlamp switch. When the dimmer switch is placed in a desired brightness position, reference voltage is applied through the dimmer switch rheostat and the I/P lamps dimmer switch signal circuit to the BCM. The BCM interprets this voltage signal, then applies a pulse width modulated (PWM) voltage through the instrument panel lamp dimming control circuit and the LED backlighting dimming control circuit illuminating all backlighting lamps.

Schematic Reference

Interior Lights Dimming Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Interior Lighting Systems Description and Operation

Electrical Information Reference

Scan Tool Reference

Control Module References for scan tool information

Ignition ON, observe the scan tool Dimming Control Signal parameter while operating the dimmer switch from high to low. The reading should change from a high percent to a low percent as the switch is rotated.

Dimmer Switch Circuit Test

1. Ignition OFF, disconnect the harness connector at the headlamp switch.
2. Ignition OFF, verify that a test lamp illuminates between the ground circuit terminal 8 and B+.

⇒	If the test lamp does not illuminate, test the ground circuit for an open/high resistance.

3. Ignition ON, test for B+ between the voltage reference circuit terminal 15 and ground.

⇒	If less than the specified value, test the voltage reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM.

4. Ignition ON, verify the scan tool Dimming Control Signal parameter is less than 0.2 volts.

⇒	If greater than the specified range, test the signal circuit terminal 13 for a short to voltage. If the circuit tests normal, replace the BCM.

5. Install a 3A fused jumper wire between the signal circuit terminal 13 and the voltage reference circuit terminal 15. Verify the scan tool Dimming Control Signal parameter is greater than 2.75 volts.

⇒	If less than the specified range, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM.

6. If all circuits test normal, test or replace the headlamp switch.

Interior Backlighting Circuit Test

1. Ignition OFF, disconnect the harness connector at the component with the inoperative backlighting.
2. Verify that a test lamp illuminates between the appropriate ground circuit terminal listed below and B+.

•	Headlamp Switch terminal 8

•	Rear Heater Switch terminal B

•	Front Auxiliary HVAC Control Panel terminal B

•	Rear Auxiliary HVAC Control Panel terminal B

•	Tow/haul Switch terminal C

•	SIR Disable Switch terminal F

•	Electronic Traction Control Switch

•	Driver Door Window Switch terminal F

•	Driver Power Lock Switch terminal B

•	Passenger Door Window Switch terminal C

•	Passenger Power Lock Switch terminal B

•	Radio terminal 8 X1

•	Driver Information Display Switch terminal 5

•	Left Steering Wheel Controls terminal 8

•	Right Steering Wheel Controls terminal 1

⇒	If the test lamp does not illuminate, test the ground circuit for an open/high resistance.

3. Connect a test lamp between the appropriate control circuit terminal listed below and ground.

Incandescent Dimming

•	Headlamp Switch terminal 7

•	Tow/haul Switch terminal B

•	Traction Control Switch terminal D

•	HVAC Control Module terminal C

•	Driver Door Window Switch terminal B

•	Driver Power Lock Switch terminal C

•	Auxiliary Blower Motor Switch terminal A

•	Passenger Door Window Switch terminal B

•	Passenger Power Lock Switch terminal C

•	Rear Auxiliary HVAC Control Panel terminal A

•	Front Auxiliary HVAC Control Panel terminal A

LED Dimming

•	Left Steering Wheel Control Switch terminal 6

•	Right Steering Wheel Control Switch terminal 2

•	Inflatable Restraint I/P Module Disable Switch terminal D

•	Driver Information Center (DIC) Switch terminal 4

•	Radio terminal 7 X1

4. Ignition ON, command the appropriate Incandescent Dimming or LED Dimming ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.

⇒	If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the BCM.

⇒	If the test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM

5. If all circuits test normal, test or replace the inoperative backlighting component.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.